Study Finds Tongue May Hold Clue to Obesity

Neuroscientists at Penn State have done a study that links taste to body weight, claiming that fat on a body could hook the brain on junk food.

They did a study on rats and found that over time, obesity numbs the taste sensation to sweet foods, causing them to consume larger quantities.

"When you have a reduced sensitivity to palatable foods, you tend to consume it in higher amounts," said Andras Hajnal, associate professor of neural and behavioral sciences at Penn State College of Medicine. "It is a vicious circle."

While previous studies have shown that obese people are less sensitive to sweet tasting foods, not much is known about the sense and pleasure obese people get from food compared to normal-weight people.

Researchers decided to find this out and studied the taste responses of two strains in the groups of rats - OLETF and LETO. The LETO rats were lean and healthy, while OLETF rats were obese.

They found that the taste responses in OLETF rats were the same as those of obese humans. While the OLETF rats started out at a normal body weight, but tend to overeat because of a missing satiety signal, which causes them to become overweight and develop diabetes. The obese rats showed a greater interest in sweet foods and also worked harder to obtain one as a reward.

"When you have excess body weight, the brain is supposed to tell you not to eat more, or not choose high caloric meals" said Hajnal. "But this control apparently fails and thus the obesity epidemic is rising, and we want to find out how the sense of taste drives up food intake."

The researchers implanted electrodes into the brains of rats and exposed them to various tastes. They recorded the firing of nerve cells during this time to determine the responses of the rats to these different tastes.

"We found that compared to the LETO rats, the OLETF rats had about 50 percent fewer neurons firing when their tongues were exposed to sucrose, suggesting that obese rats are overall less sensitive to sucrose," explained Hajnal. "These findings tell us that there is a difference in activation of neurons between lean and obese rats when they are exposed varying concentrations of sucrose. If you sense sweetness less, you may be inclined to eat sweeter foods."

The researchers believe that by eating more sweet foods over time, the brain’s reward center could be changed by giving the body weaker nerve signals, thus affecting the taste of foods.

This study was published in a recent issue of the Journal of Neurophysiology.

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